STUDY OF DENSITY AND ORIENTATION IN POLY(ETHYLENE-TEREPHTHALATE) USING FOURIER-TRANSFORM RAMAN-SPECTROSCOPY AND MULTIVARIATE DATA-ANALYSIS

Partial Least Squares modelling techniques have been used to calibrate Raman spectra in terms of the density of poly(ethylene terephthalate) , with a standard prediction eff or of 0.0024 g cm-3. The calibration, which utilizes, primarily, the bands at approximately 1730, 1094, 997 , and 860 cm-1, spans isotropic, uniaxial and biaxially oriented sampl es with a single model; this is superior to univariate calibrations wh ich require separate models for isotropic and oriented samples. Hierar chical Cluster Analysis and Principal Components Analysis were also us ed for exploratory analysis of the spectra; these methods grouped samp les in terms of their density and orientation characteristics, and als o identified the bands which responded most significantly to morpholog y changes. It was shown that the 1615 cm-1 ring-stretching mode differ entiated the samples on a basis other than simply by density or orient ation alone; further work, however, is needed to understand this behav iour. The potential power of multivariate analysis techniques for corr elating Raman spectra and polymer morphology was clearly demonstrated.